Domestic and non-domestic properties require utilities such as power, water, water heating and sewage disposal. Most properties rely upon connection to reticulated services, which cannot be available to all prospective building locations, especially those beyond urban centres. The infrastructure for the provision of such services cannot meet increasing demand, nor can it continue to be expanded infinitely. Additionally, provision of these utilities to remote locations is inefficient and costly. Furthermore, the provision of utility services from centralised plants can also be vulnerable to disruption through natural disaster and infrastructure failure. Damage to a centralised plant can potentially have a significant impact to a large portion of a population if they are all interconnected to the same plant.
Power Supply
Conventional power supply comes from centralised, large scale power generation stations, with electricity reticulated to the population centres via transmission and distribution networks. Power demand increases continuously, requiring increased capacity for this capital intensive infrastructure. Long term planning requirements are based upon estimated projections and are removed from the decision making at a local level where the drive for capacity growth is typically generated.
Also, meeting short term peak demand levels often comes at a high marginal cost. Power supply contracts to the user are becoming more weighted to fixed line charges over variable consumption charges in order to provide investment certainty in power generation and transmission network capacity. This indirect supply vs. consumption relationship diminishes the incentive for energy efficiency at the user level.
The majority of power generation relies upon fossil fuelled thermal power, which carries with it the consequence of greenhouse gas emissions. Biofuels are generally uncompetitive for large scale centralised power generation, and renewable alternatives are less manageable and less developed and cannot be relied upon for base load generation.
On-site power generation is a long-established alternative, using engine driven generators. These are typically unsophisticated in their performance, use management and are generally a last-resort option. Improvements are emerging, such as home sized Stirling engine and gas turbine systems, invariably fossil fuelled, which can provide combined heat and power to the property if configured appropriately. Further, none of these power generation systems have been designed to interact with household water and wastewater systems for the purpose of sanitising and recirculating water to the household.
Solar and wind power systems for individual dwellings are also becoming popular, and are acceptable options for low intensity energy capture/generation. However, there is no guarantee for continuity in supply or matching demand using these systems, nor can they economically provide for high power and peak load demands.
Wastewater Treatment
Centralised sewage treatment, where each property is connected to the sewer system for conveyance to a large centralised wastewater treatment plant (“WWTP”), is relatively common in most urban centres. Various treatment processes are utilised to treat wastewater, with biological processes, more particularly activated sludge processes, being the predominant methods.
Until recently, most treated sewage effluent was discharged to local receiving waters or the ocean. More recently there has been a trend to add tertiary treatment processes to the basic activated sludge process to improve effluent quality and allow indirect reuse of the effluent via subsurface injection into aquifers or recycle to dams, which are used as a source of drinking water.
Excess sludge from large centralised WWTPs is usually mechanically dewatered and then disposed either to landfill or used in agriculture as a fertiliser supplement. In highly populated urban areas, excess sludge is often incinerated as the preferred disposal option. Today, most large centralised WWTPs produce two adverse discharges to the environment, that is, the treated effluent and excess sludge. The wastewater and sludge treatment/disposal processes are fairly significant generators of greenhouse gases, both carbon dioxide and methane in particular, being generated over time from sludge which is land applied or landfilled.
Centralised wastewater treatment is expensive and installation of reticulation systems is becoming more of a constraint in new urban developments. With the emergence of reliable membrane-based treatment processes there is now a global trend to more decentralised wastewater treatment systems.
The most common single dwelling wastewater treatment process is the septic tank system. This involves no mechanical components but requires large vessels for crude biological treatment of the wastewater and retention of the sludge, which is typically pumped out about once every 5 years or so, for landfill disposal elsewhere. The effluent from the septic tanks is then typically sub-surface irrigated in a French drain system, with the wastewater often ultimately discharging to receiving waters. In many parts of the world these discharges have caused severe environmental impacts in the receiving waters, predominately through eutrophication of the water body from the nutrients associated with the wastewater.
To overcome some of these problems aerobic treatment units (“ATUs”) are often provided. These are small mechanical biological treatment units that provide a higher level of wastewater treatment than septic tanks but they still rely on disposal of the contaminated effluent to the environment, often again reaching sensitive water bodies. These ATUs require routine maintenance and monitoring to ensure they are working to design specifications and generally involve large tankage requirements, typically in the order of many thousands of litres. There is also concern regarding greenhouse gas emissions, especially methane from any uncontrolled anaerobic digestion.
The operating efficiency of the biological processes common to all these treatment systems can be highly sensitive to their maintenance and operating conditions, and especially to excessive loadings of commonly used household chemical products.
In sensitive ecological environments, disposal of treated wastewater to local water bodies, often via percolation through the ground, is not acceptable. There is thus a need for a reliable and robust wastewater treatment process, for single-dwelling applications, where the wastewater can be treated to a level to allow reuse and hence eliminate any adverse discharge to the environment. It is necessary that this be achieved at moderate cost.
The lack of possible connection to centralised wastewater treatment schemes is often the major limitation in local authority approval to release rural land for residential development, especially single sites.
Water Conservation
An increasing global concern is the finite supply of water, with increasing demand on a limited supply as drawn from the local, natural environment. Conventional housing developments expect to be connected to a reticulated utility supply, all necessarily treated to a potable quality, although, only a small proportion of the water is actually used for drinking purposes.
Those located outside urban areas may not have access to mains water supplies. This may require them to either draw from a natural water course, or aquifer, or rely upon roof collected rainwater. In addition to locational constraints each option poses quality and quantity issues in assuring continuity of supply. Water conservation can be practiced with installations specifically designed for economy in use, but there is no existing method for on-site recycling of black wastewater as the means to reduce net consumption.
U.S. Pat. No. 4,052,858 discloses the utilisation of a waste heat stream from a power source to sterilise water. However, the method provided in this document does not provide the means for the on-site sterilisation of wastewater to “white water” quality, and its subsequent reintegration with a primary water supply. Furthermore, this document does not disclose the separation and treatment of sludge or the utilisation of waste heat for water, building or space heating. That is, the wastewater treatment systems of the prior art do not disclose a fully integrated system which provides for the on-site recirculation and reuse of water and energy.
The integrated utility system of the present invention has one object thereof to overcome substantially the abovementioned problems of the prior art or at least provide a useful alternative thereto.
The discussion of the background art is included exclusively for the purpose of providing a context for the present invention. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was common general knowledge in the field relevant to the present invention in Australia or elsewhere before the priority date.
Throughout the specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
Throughout the specification, the term “power supply” is understood to refer to an electrical power generating system including, but not limited to engine/generators, solar and wind power generators and burner/boiler thermal power generators.
Throughout the specification the term “waste energy” is understood to refer to any one or more of the by-product thermal energy or excess electrical energy from the power supply.